I'm working on my Mac for video editing from time to time and normaly use Windows and Linux. Thinking about to switch completely but there is one thing I'm so darn used to which held me back for years now.

On Windows or Linux taskbar (e.g. Avant Window Navigator) you click the app icon and the app and it's windows come to front. Now comes the important part!! IF you click a second time on the app icon the app (window) goes back to the taskbar, minimizes itself....

Is there any dock tweak or app which can do this??? I desperately need this as I'm used to this way for decades.

Right-click on your Dock, and select Dock Preferences (found in System Preferences). From here, select Minimize windows into application icon. As it says, all windows of said application will store in that icon on the Dock. From here, Exposé will show a separate pane when activated that will present you wish the minimized content.